In a beamforming system, at a transmit end, after being multiplied by a transmitting weight vector w, transmitted signals are transmitted to a radio channel by using different antenna array elements; and, at a receive end, received signals of the antenna array elements are transmitted to a signal processing module after weighted vector summation of a receiving weight c is performed. Forming of a target beam is categorized into an adaptive beamforming technology and a beam switching technology. The adaptive beamforming technology is to obtain an optimal beam mode after a series of operations, that is, an antenna weighted vector w, are performed on a signal received by an array antenna, and use the optimal beam mode for communication. Although the adaptive beamforming may be optimal in theory, its computing complexity is high and its convergence speed is slow. Therefore, a beam switching technology is introduced in order to reduce implementation difficulty. The beam switching technology refers to forming a beam codebook matrix W=(w0, w1, . . . , wK) after the antenna weighted vector w required for beamforming is predefined and has a fixed value in a device, so that the device only needs to search for the weighted vector in beam codebook space during practical communication. Currently, the beam switching technology is widely applied in millimetric wave communications. All 60 GHz millimetric wave communications standards (IEEE802.15.3c, IEEE802.11ad, Chinese standards, and the like), which are currently released or under development, support the beam switching technology that is based on a fixed beam codebook.
The currently released standard IEEE802.15.3c stipulates the beam codebook matrix W. Formula (1) is a formula for generating an element in a pth row and a qth column in the IEEE802.15.3c codebook matrix W, that is, a pth-dimension element in a codebook vector wq of a qth beam, where M is the number of the antenna array elements, K is the number of beams (K≧M, generally K=2M). Formula (1) denotes an N-phase codebook, where the codebook may use more fine-grained phases to generate a beam that has a higher main lobe gain and a lower side lobe level. In the formula, N is the number of phases.
                                          W            ⁡                          (                              p                ,                q                            )                                =                      ⅇ                          j              ⁢                                                2                  ⁢                  π                                N                            ⁢                              fix                ⁡                                  (                                                                                    p                        ×                                                  mod                          ⁡                                                      (                                                          q                              +                                                              K                                /                                2                                                                                      )                                                                                              ,                      K                                                              K                      /                      N                                                        )                                                                    ,                                  ⁢                  p          =          0                ,        1        ,        …        ⁢                                  ,                              M            -            1                    ;                      q            =            0                          ,        1        ,        …        ⁢                                  ,                  K          -          1                                    (        1        )            
In a case in which the beam codebook is known (in a case in which formula (1) is known), the device can, during practical communication, obtain a sufficient antenna gain simply by searching for an optimal beam pair in a specific manner.
To improve beam search efficiency and reduce time consumption and energy consumption in a beam search process, a fast beam search algorithm is submitted to related Chinese 60 GHz millimetric wave communications standards. The algorithm first creates a model of a beam search issue by treating it as an optimization issue, and then uses sequence numbers of beams of both the transmit and receive ends as independent variables and uses strength or a signal-to-noise ratio of a received signal as a target function to obtain optimized search space. The fast beam search algorithm takes advantage of beam width difference generated by different numbers of the antenna array elements, and accelerates the beam search process based on a dichotomic search idea and a dichotomy policy. A currently used basic process of the fast beam search algorithm is as follows:
(a) Set the number of activated antenna array elements to m=2 and deactivate the remaining M−2 antenna array elements, perform beam search (in this case, the beams are relatively wide, the search space is relatively small, and a traverse method may be used) to obtain a current optimal beam pair, record a main lobe direction (f, φ) of an optimal beam, and record a search counter as i=1.
(b) Set i=i+1, set the number of activated antenna array elements to m=2i and set the number of deactivated antenna array elements to M−2i, use beams close to the currently recorded optimal main lobe direction (f, φ) as an initial beam pair to continue the beam search and obtain an optimal beam pair, and update the record of the main lobe direction (f, φ) of the optimal beam.
(c) If all antenna array elements are put into use (m=M), end the search and use the currently recorded optimal beam pair as a final search result; otherwise, return to step (b).
It can be learnt from the foregoing description that, when the beam codebook is calculated by using formula (1) currently, in order to implement beam search, activation and deactivation control needs to be performed separately on each antenna array element of a phased array antenna until all antenna array elements are in an activated state, which undoubtedly increases hardware implementation difficulty and is adverse to algorithm implementation.